Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Other	$ 413		$ 413
Deferred Tax Assets, Tax Credit Carryforwards	2		8
Income Tax Examination, Penalties and Interest Expense	1	$ 0	1	$ 0
Income Tax Examination, Interest Accrued	0	$ 0	0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	0		0
Income Tax Examination, Penalties Accrued	$ 0		0
UNITED STATES
Operating Loss Carryforwards [Line Items]
Deferred Other Tax Expense (Benefit)			225
UNITED KINGDOM
Operating Loss Carryforwards [Line Items]
Deferred Other Tax Expense (Benefit)			1
Alternative Minimum Tax (AMT) [Member]
Operating Loss Carryforwards [Line Items]
Proceeds from Income Tax Refunds			$ 421